Method for producing coated mineral shaped bodies

ABSTRACT

The invention relates to a method for producing coated mineral shaped bodies by applying an aqueous coating agent containing a polymer dispersion serving as a bonding agent and at least one aqueous styrene maleic anhydride copolymer solution. The shaped body is subsequently hardened and the coating agent is dried. The invention is characterized in that the at least one aqueous styrene maleic anhydride copolymer solution is added to the polymer dispersion after completion of the polymerization. The shaped bodies coated in such a manner exhibit an improved efflorescence behavior. The method is particularly suited for coating roofing tiles and fibrated concrete slabs.

The invention relates to a process for producing coated mineralmoldings, which comprises using, for the coating process, aqueouscoating compositions which comprise at least one styrene-maleicanhydride copolymer. The resultant coated moldings have improvedefflorescence behavior. The process is particularly suitable for thecoating of roofing tiles and of fiber-filled cement panels.

In producing concrete roofing tiles, an appropriately molded mortar massis generally coated, prior to setting, with an emulsion paint to imparta color. The subsequent setting is then carried out together with thedrying of the paint at temperatures of from 40 to 100° C. After thesetting process, there may be a second coating process with an emulsionpaint or with a clear lacquer. The task of the emulsion paint, besidescoloring, is to prevent lime efflorescence during the setting of theconcrete roofing tiles.

In order that the paint does not coagulate on the unset concrete, whichis termed green concrete, a certain degree of cement-compatibility andsalt resistance is required from the binder present in the paint. Thisis generally achieved by using ionic and/or nonionic emulsifiers, andalso by using functional monomers, e.g. methacrylic acid, acrylic acid,maleic acid, acrylamide, methacrylamide, ethenesulfonate, sulfoxyalkylmethacrylate, or acrylamidoalkylsulfonic acids.

Another task for the emulsion paint is to prevent or reduce soiling, andin particular algal growth, on the finished roofing tiles.

EP-A-0 894 780 describes radiation-cured coatings for mineral moldingswith improved resistance to efflorescence, but their production requiresrelatively high levels of technical resource and is relatively costly.

EP-A-0 754 663 describes the coating of cement-like substrates, theefflorescence behavior being improved by foaming the coatings onto thesubstrates, using aliphatic (C₁₂-C₂₄) carboxylic acids as foamingagents.

EP-A-0 469 295 describes coatings whose efflorescence behavior isimproved by the use of emulsifiers based on sulfonated diaryl ethers.

WO 99/48841 describes the use of carboxymethylcellulose as protectivecolloid to prepare dispersions with good resistance to efflorescence andadequate stability.

WO 97/15604 describes styrene-acrylate latices which are prepared byemulsion polymerization of styrene and acrylates in the presence of astyrene-maleic anhydride copolymer, and are suitable for preparingsolvent-free paints.

Surprisingly, it has now been found that when mineral moldings arecoated with an aqueous coating composition comprising a polymerdispersion as binder, the efflorescence behavior of the coated moldingsis improved if the polymer dispersion comprises at least onestyrene-maleic anhydride copolymer solution which is added to thepolymer dispersion after conclusion of the polymerization.

The present application therefore provides a process for preparing an atleast partially coated mineral molding, by applying an aqueous coatingcomposition comprising a polymer dispersion as binder and comprising atleast one aqueous styrene-maleic anhydride copolymer solution to atleast part of the surface of the molding, followed by setting of themolding and drying of the coating composition, which comprises addingthe at least one aqueous styrene-maleic anhydride copolymer solution tothe polymer dispersion after conclusion of the polymerization.

For the purposes of the present invention, examples of these moldingsare stones, tiles, concrete blocks, roofing tiles, panels, pipes, andsculptures.

The coating composition may be applied by any of the techniques familiarto the skilled worker.

The setting of the molding and drying of the coating compositionpreferably takes place at temperatures of from 40 to 100° C.

Based on solids content, the polymer dispersions preferably comprisefrom 0.5 to 5% by weight, particularly preferably from 1 to 3% byweight, of styrene-maleic anhydride copolymers.

The styrene-maleic anhydride copolymer solutions here are preferablyprepared by stirring the styrene-maleic anhydride copolymers into water,and dissolving these by adding a solution of an alkali, e.g. ammonia,monoethanolamine, sodium hydroxide, and/or potassium hydroxide, attemperatures of from 20 to 100° C. The pH of the finished solution ispreferably >8.

Suitable styrene-maleic anhydride copolymer solutions also includecommercially available solutions, e.g. SMA 1000 HNa®, SMA 2000 HNa®, SMA3000 HNa® and SMA 4000 HNa® (Elf Atochem).

The polymer dispersions are preferably based on polymers which contain

a) from 85 to 100% by weight, particularly preferably from 85 to 99.8%by weight, of esters of acrylic acid with C₁-C₁₂ alkanols, e.g. ethylacrylate, butyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate,esters of methacrylic acid with C₁-C₁₂ alkanols, e.g. methylmethacrylate, butyl methacrylate, cyclohexyl methacrylate, and isobornylmethacrylate, and/or vinylaromatic monomers, such as styrene andvinyltoluene,

b) from 0 to 5% by weight, particularly preferably from 0.2 to 5% byweight, of stabilizing monomers, and

c) from 0 to 10% by weight of other monomers.

Preference is given here to those combinations of softening monomers,e.g. butyl acrylate and 2-ethylhexyl acrylate, and of hardeningmonomers, e.g. methyl methacrylate and styrene, which give the polymersa glass transition temperature which is preferably in the range from −10to 60° C., particularly preferably in the range from −5 to 45° C., andin particular in the range from 0 to 30° C.

Preferred monomers a) are esters of acrylic acid with C₁-C₁₂alkanolsand/or styrene.

Preferred stabilizing monomers b) are carboxylic acids, e g. acrylicacid, methacrylic acid, and itaconic acid, carboxamides, e.g.acrylamide, methacrylamide, phosphates, e.g. (meth)acryloyloxyalkylphosphates, phosphonates, sulfates, sulfonates, e.g. sodiumethenesulfonate, sulfoalkyl (meth)acrylates, e.g. the potassium salt ofsulfopropyl methacrylate (SPM®, from the company Raschig), and/orsulfoalkyl(meth)acrylamides, e.g. the sodium salt ofacrylamido-2-methylpropanesulfonic acid (AMPS®, from the companyLubrizol).

Preferred monomers c) are keto-group-containing monomers, e.g.acetoacetoxy-group-containing monomers, copolymerizable derivatives ofdiacetone, e.g. diacetoneacrylamide and diacetonemethacrylamide,copolymerizable silanes, e.g. alkoxyvinylsilanes, and(meth)acryloyloxyalkylsilanes, copolymerizable ethyleneurea derivatives,e.g. N-((meth)acryloxyethyl)-N,N′-ethyleneurea andN-(acrylamidoethyl)-N, N′-ethyleneurea, hydroxyl-group-functionalitymonomers, e.g. hydroxyalkyl (meth)acrylates, and/or epoxy-functionalitymonomers, e.g. glycidyl methacrylate.

Particularly preferred monomers c) are the acetoacetoxy-group-containingmonomers acetoacetoxyethyl methacrylate, acetoacetoxybutyl methacrylate,acrylamidomethylacetylacetone, vinyl acetoacetate, diacetoneacrylamide,and diacetonemethacrylamide.

To improve soiling behaviour, polymer dispersions which, as othermonomers c), contain keto-group-containing monomers advantageously alsocontain polyfunctional carboxylic hydrazides which have at least twohydrazide groups. It is preferable for the ratio of hydrazide groups toketo groups used to be equimolar. Particularly suitable polyfunctionalcarboxylic hydrazides are adipic dihydrazide, oxalic dihydrazide,isophthalic dihydrazide, and/or polyacrylic polyhydrazide.

Other suitable polymer dispersions are commercially available straightacrylate dispersions and styrene-acrylate dispersions, e.g. Mowilith®DM611, Mowilith® DM 777, Mowilith® LDM 7412 and Mowilith® 771 (ClariantGmbH).

The polymer dispersions may be prepared by the customery processes ofemulsion polymerization, where the monomers are emulsified in theaqueous phase in the presence of emulsifiers, initiators, and protectivecolloids, and are advantageously polymerized at temperatures of from 60to 95° C.

The emulsion polymerization may be carried out by the familiar processesknown to the skilled worker, e.g. batch processes, metered-monomerprocesses, or emulsion-feed processes. It is preferable to use theemulsion-feed process, in which a small amount of the monomers isprepolymerized and then the remainder of the monomers is metered in inthe form of an aqueous emulsion. Where appropriate, it is also possiblefor a number of different monomer emulsions to be metered in one afterthe other.

Based on the content of polymer, the dispersions preferably comprise upto 3% by weight, particularly preferably up to 2% by weight, of ionicemulsifiers, and preferably up to 6% by weight, particularly preferablyup to 4%, of nonionic emulsifiers.

Examples of suitable nonionic emulsifiers are alkyl polyglycol ethers,e.g. ethoxylation products of lauryl, oleyl, or stearyl alcohol, ormixtures of the same, e.g. coconut fatty alcohol; alkylphenol polyglycolethers, e.g. ethoxylation products of octyl- or nonylphenol,diisopropylphenol, triisopropylphenol, and di- or tri-tert-butylphenol;and ethoxylation products of polypropylene oxide.

Preferred suitable ionogenic emulsifiers are anionic emulsifiers, e.g.the alkali metal or ammonium salts of alkyl-, aryl- oralkylarylsulfonates or -phosphonates, or of alkyl, aryl, or alkylarylsulfates, or of alkyl, aryl, or alkylaryl phosphates, or compounds withother anionic end groups, and it is also possible here for there to beoligo- or polyethylene oxide units between the hydrocarbon radical andthe anionic group. Typical examples are sodium lauryl sulfate, sodiumundecyl glycol ether sulfate, sodium lauryl diglycol sulfate, sodiumtetradecyl triglycol sulfate, sodium octylphenol glycol ether sulfate,sodium dodecylbenzenesulfonate, sodium lauryl diglycol sulfate, andammonium tri-tert-butylphenol penta- and octaglycol sulfate.

For initiation and further conduct of the polymerization, use may bemade of oil- or water-soluble free-radical generators or redox systems.Examples of those suitable are hydrogen peroxide, potassiumperoxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate,dibenzoyl peroxide, lauryl peroxide, tri-tert-butyl peroxide,bisazodiisobutyronitrile, alone or together with reducing components,e.g. sodium bisulfite, Rongalit, glucose, ascorbic acid, or otherreducing compounds. It is preferable to use peroxodisulfates.

In the polymerization use may also be made of regulators, e.g.mercaptans, in particular N-dodecyl mercaptan, thiophenol, and2-methyl-5-tert-butylthiophenol, in amounts of up to 1% by weight,preferably up to 0.5% by weight. However, it is advantageous to avoidthe use of regulators.

If the emulsion polymerization process used has two or more stages, itis advantageous for the combination of the hardening and the softeningmonomers and the ratio of the phases to be such that the dispersion hasa minimum film-forming temperature in the range from 0 to 50° C. andthat the resultant films of dispersion have an elongation at breakof >150% at a film thickness of 100 μm.

The pH of the dispersions is preferably set to 6.5-10, particularlypreferably 7.0-9.0. Examples of bases suitable for this purpose areaqueous solutions of the hydroxides of ammonia, of alkali metals, or ofalkaline earth metals. It is also possible to use buffers, e.g. sodiumhydrogenphosphate, sodium acetate, or sodium hydrogencarbonate, and,where appropriate, these may be used during the emulsion polymerizationitself.

Where appropriate, the coating compositions also comprise film-formingauxiliaries, e.g. white spirit, Texanol®, butyl glycol, butyl diglycol,butyl dipropylene glycol, and butyl tripropylene glycol, plasticizers,e.g. dimethyl phthalate, dibutyl phthalate, diisobutyl adipate,dispersing agents, e.g. polyacrylic acids and appropriate copolymers,e.g. Lopon® 890, Dispex® G40, thickeners, e.g. those based onpolyacrylates and on polyurethanes, e.g. Borchigel® L75 and Tafigel® PUR60, emulsifiers, stabilizers, protective colloids, preservatives,antifoams, e.g. mineral oil antifoams and silicone antifoams, wettingagents, e.g. aminomethylpropanol, fillers, e.g. calcite, chalk, powderedquartz, and baryte, pigments, e.g. iron oxide red, black pigments, andorganic pigments, and/or other additives usual for formulating coatingcompositions.

The desired viscosity of the coating compositions may be set by addingwater and/or using thickeners.

One embodiment carries out the process in such a way that, following thesetting of the molding and drying of the coating composition, anotherlayer of the same coating composition or of another coating compositionis applied to the molding, and then the coating composition is driedand, where appropriate, the process is then repeated one or more times.

The process of the invention is particularly suitable for the coating ofroofing tiles or of fiber-filled cement panels.

The coating compositions are preferably roofing tile paints.

The invention also provides moldings which are produced by the processdescribed above.

The examples below serve to illustrate the invention, but do notrestrict the same.

EXAMPLES 1 TO 8 Preparation of Polymer Dispersions ComprisingStyrene-maleic Anhydride Copolymer Solutions EXAMPLE 1

20 g of a 25% strength styrene-maleic anhydride copolymer solution, SMA3000 HNa® (Elf Atochem), are stirred into 1000 g of Mowilith® DM 611styrene-acrylate dispersion (Clariant GmbH, solids content about 50%).

EXAMPLE 2

20 g of the 25% strength styrene-maleic anhydride copolymer solution SMA3000 HNa® (Elf Atochem) are stirred into 1000 g of Mowilith® DM 777styrene-acrylate dispersion (Clariant GmbH, solids content 46%).

EXAMPLE 3

20 g of the 25% strength styrene-maleic anhydride copolymer solution SMA3000 HNae (Elf Atochem) are stirred into 1000 g of Mowilith® LDM 7412styrene-acrylate dispersion (Clariant GmbH, solids content about 46%).

EXAMPLE 4

20 g of the 25% strength styrene-maleic anhydride copolymer solution SMA3000 HNa® (Elf Atochem) are stirred into 1000 g of Mowilith® LDM 771styrene-acrylate dispersion (Clariant GmbH, solids content 50%).

EXAMPLE 5

A dispersion is prepared as follows:

Using a high-speed stirrer, a monomer emulsion composed of: 965.6 partsby weight of water 185.7 parts by weight of a 28% strength solution of aC₁₂-C₁₄-alkyl polyglycol ether sulfate having about 3 ethylene oxideunits  26.0 parts by weight of methacrylic acid  15.6 parts by weight ofacrylic acid  3.0 parts by weight of ammonium peroxodisulfate is stirredinto a mixture composed of: 2808 parts by weight of methyl methacrylateand 2392 parts by weight of butyl acrylate,

and stirring is continued until a stable emulsion is produced. 2470parts by weight of water, 9.3 parts by weight of a 28% strength solutionof a C₁₂-C₁₄-alkyl polyglycol ether sulfate having about 3 ethyleneoxide units, and 312 parts by weight of the monomer emulsion are thenheated to 80° C. in a suitable reaction vessel, and treated with asolution of 2.6 parts by weight of ammonium peroxodisulfate in 69.4parts by weight of water. The remaining monomer emulsion is then meteredwithin a period of 3.5 hours. Heating is continued for a further 60minutes, followed by cooling. The pH of the dispersion is set to 9.0,using 12.5% strength ammonia solution. The solids content of thedispersion is about 52.7%, and the minimum film-forming temperature MFTis about 14° C.

EXAMPLE 6

20 g of a 25% strength styrene-maleic anhydride copolymer solution, SMA3000 HNa® (Elf Atochem), are stirred into 1000 g of the dispersion fromExample 5.

EXAMPLE 7

A dispersion is prepared as follows:

Using a high-speed stirrer, a monomer emulsion composed of: 589.3 partsby weight of water  53.6 parts by weight of a 28% strength solution of aC₁₂-C₁₄-alkyl polyglycol ether sulfate having about 3 ethylene oxideunits  45.0 parts by weight of AMPS R ® 2430 solution (Lubrizol)  3.0parts by weight of sodium hydrogencarbonate  4.5 parts by weight ofsodium peroxodisulfate is stirred into a mixture composed of: 810 partsby weight of methyl methacrylate and 690 parts by weight of butylacrylate,

and stirring is continued until a stable emulsion is produced. 712.5parts by weight of water, 2.7 parts by weight of a 28% strength solutionof a C₁₂-C₁₄-alkyl polyglycol ether sulfate having about 3 ethyleneoxide units, and 90 parts by weight of the monomer emulsion are thenheated to 80° C. in a suitable reaction vessel, and treated with asolution of 0.75 parts by weight of sodium peroxodisulfate in 7.5 partsby weight of water. The remaining monomer emulsion is then meteredwithin a period of 3.5 hours. Heating is continued for a further 60minutes, followed by cooling. The solids content of the dispersion isabout 52%, and the minimum film-forming temperature MFT is 16° C.

EXAMPLE 8

20 g of a 25% strength styrene-maleic anhydride copolymer solution, SMA3000 HNa® (Elf Atochem), are stirred into 1000 g of the dispersion fromExample 7.

EXAMPLES 9 and 10 Preparation of Color Pastes EXAMPLE 9

A color paste for roofing tile paints is prepared by introducing  18.0 gof Lopon ® 890 (BK Giulini) dispersing agent  6.0 g of AMP 90 ® (AngusChemie GmbH) wetting agent  3.0 g of Mergal ® K 14 (Troy) preservativein 328 g of water, and a dissolver is used to disperse the following, insuccession, into the mixture  75.0 g of China Clay B ®(ECCInternational) 630.0 g of Omyacarb ® 5 GU (Omya) 180.0 g of iron oxideblack  4.5 g of Tylose ® H 300 (Clariant GmbH).

EXAMPLE 10

A color paste is prepared by using a dissolver to stir 200 g of calcitefilter and then 50 g of iron oxide red pigment into 100 g of water.

EXAMPLES 11 to 16

Preparation of paints: coating of Eterplan panels, and assessment ofefflorescence behavior (comparative examples 12, 14 and 16)

Paints are prepared by using a laboratory stirrer to stir together thecomponents given in Table 1 in succession in the sequence given. Thepaints are then doctored at 300 μm wet thickness onto Eterplan panelsand dried for 24 hours at room temperature. Before this, the Eterplanpanels were painted with a 33% strength CaCl₂ solution and dried for 24hours at room temperature, in order to promote efflorescence. Thepainted panels are then stored for 7 days, with the coated side above awater bath heated at 60° C., in order to promote efflorescence. Thepanels are then dried at room temperature and the efflorescenceassessed. The results are given in Table 1.

Table 1 shows that adding a styrene-maleic anhydride copolymer solutionimproves the efflorescence behavior of the paints.

EXAMPLES 17 to 22

Preparation of paints, coating of Eterplan panels, and assessment ofefflorescence behavior (comparative examples 18, 20 and 22)

Paints are prepared by using a laboratory stirrer to stir together thecomponents given in Table 2 in succession in the sequence given. Thepaints are then doctored at 300 μm wet thickness onto Eterplan panelsand dried for 24 hours at room temperature. Before this, the Eterplanpanels were painted with a 33% strength CaCl₂ solution and dried for 24hours at room temperature, in order to promote efflorescence. Thepainted panels are then stored for 7 days, with the coated side above awater bath heated at 60° C., in order to promote efflorescence. Thepanels are then dried at room temperature and the efflorescenceassessed.

Table 2 shows that adding a styrene-maleic anhydride copolymer solutionimproves the efflorescence behavior of the paints.

TABLE 1 Example 12 Example 14 Example 16 Example 11 (Comparison) Example13 (Comparison) Example 15 (Comparison) Dispersion 193 g of 193 g ofMowilith ® 187 g of 187 g of 194 g of 194 g of dispersion from DM 611dispersion from Mowilith ® dispersion from Mowilith ® LDM example 1(styrene-acrylate example 2 DM 777 example 3 7412 dispersion, Clariant(straight (straight GmbH) acrylate acrylate dispersion, dispersion,Clariant GmbH) Clariant GmbH) Paste 140 g of paste 140 g of paste from140 g of paste 140 g of paste 140 g of paste 140 g of paste from example9 example 9 from example 9 from example 9 from example 9 from example 9Butyl diglycol 7 g 7 g 2 g 2 g Water 3 g 3 g 1 g 1 g White spirit 2 gDimethyl 2 g phthalate Polyurethane 0.33 g 0.33 g 0.26 g 0.26 gthickener Silicone antifoam 1.2 g 1.2 g 1.2 g 1.2 g 1.2 g 1.2 gEfflorescence none slight none marked slight marked

TABLE 2 Example 18 Example 20 Example 22 Example 17 (Comparison) Example19 (Comparison) Example 21 (Comparison) Dispersion 187 g of 187 g of 187g of 187 g of 500 g of 500 g of dispersion from Mowilith ® dispersionfrom dispersion from dispersion from dispersion from example 4 DM 771example 6 example 5 example 8 example 7 (straight acrylate dispersion,Clariant GmbH) Paste 140 g of paste 140 g of paste 140 g of paste 140 gof paste 350 g of paste 350 g of paste from example 9 from example 9from example 9 from example 9 from example 10 from example 10 Butyldiglycol 7 g 7 g 7 g 7 g 18 g 18 g Water 3 g 3 g 3 g 3 g 9 g 9 g Whitespirit Dimethyl phthalate Polyurethane 0.33 g 0.33 g 0.23 g 0.23 gthickener Silicone antifoam 1.2 g 1.2 g 1.2 g 1.2 g 3.1 g 3.1 gEfflorescence none slight none slight none slight

What is claimed is:
 1. A process for producing an at least partiallycoated mineral molding, said process comprising: applying an aqueouscoating composition comprising a polymer dispersion as binder andcomprising at least one aqueous styrene-maleic anhydride copolymersolution to at least part of a surface] of a mineral molding, settingthe mineral molding and drying the aqueous coating composition, whereinthe at least one aqueous styrene-maleic anhydride copolymer solution isadded to the polymer dispersion after conclusion of the polymerizationof the polymer dispersion.
 2. The process as claimed in claim 1,wherein, based on solids content, the aqueous coating compositioncomprises from 0.5 to 5% by weight of styrene-maleic anhydridecopolymer.
 3. The process as claimed in claim 1, wherein the polymerdispersion is based on a polymer comprising monomers: a) from 85 to 100%by weight of a monomer selected from the group consisting of esters ofacrylic acid with C₁-C₁₂ alkanols, esters of methacrylic acid withC₁-C₁₂ alkanols, vinylaromatic monomers, and mixtures thereof, b) from 0to 5% by weight of stabilizing monomers, and c) from 0 to 10% by weightof other monomers, where the glass transition temperature T_(g) of thepolymer is from −10 to 60° C.
 4. The process as claimed in claim 3,wherein the monomers a) are esters of acrylic acid with C₁-C₁₂ alkanolsand/or styrene.
 5. A process as claimed in claim 3, wherein the monomersb) are monomers selected from the group consisting of carboxylic acids,carboxamides, phosphates, phosphonates, sulfates, land/on sulfonates,and mixtures thereof.
 6. The process as claimed in claim 3, wherein themonomers c) are monomers selected from the group consisting ofketo-group-containing monomers, copolymenizable derivatives ofdiacetone, copolymenizable silanes, copolymerizable ethyleneureaderivatives, and mixtures thereof.
 7. The process as claimed in claim 1,wherein the coating composition further comprises components selectedfrom the group consisting of film-forming agents, dispersing agents,thickeners, emulsifiers, protective colloids, stabilizers,preservatives, antifoams, wetting agents, pigments, fillers, andmixtures thereof.
 8. The process as claimed in claim 1, furthercomprising following the setting of the mineral molding and drying ofthe aqueous coating composition, applying another layer of the aqueouscoating composition to the mineral molding, and drying the aqueouscoating composition and, where appropriate, repeating the applying anddrying steps one or more times.
 9. The process as claimed in claim 1,wherein the mineral molding is a roofing tile or fiber-filled cementpanel.
 10. The process as claimed in claim 1, wherein the aqueouscoating composition is a roofing-tile paint.
 11. A mineral moldingobtained by the process as claimed in claim 1.